Project Summary/Abstract Cancer affects not only those with the disease, but also their family members. Family caregivers are known to have compromised health, as the detrimental impact of patients' cancer on their caregivers is substantial. Studies have documented the patient's distress relates to the caregiver's poorer health and vice versa, suggesting that cancer caregivers' health is an interpersonal, dyadic problem. Unknown are when and how the dyadic, cross-over effects occur. Stress regulation among cancer caregivers and their patients is interdependent, as is the caregiver-patient relationship itself. This dyadic stress regulation occurs when members of a dyad mutually calm each other's stress reactions and dampen negative affect and physiological arousal (coregulation) or mutually increasing those outcomes (coagitation). We propose that greater stress coregulation protects against adverse health outcomes, whereas greater stress coagitation exacerbates them. This project will examine dyadic stress regulation between cancer caregivers and their patients, and test coregulation and coagitation as predictors of health outcomes. Coregulation/coagitation will be quantified by cardiovascular (heart rate variability: HRV), neuroendocrine (salivary cortisol), and self-reported affective reactivity and regulation, in response to a standardized stress situation that is relevant both to health and to close relationships. We will then examine prospectively the extent to which the indicators of coregulation for this discrete stressor relate to daily outcomes (mood, diurnal cortisol, and sleep) and interim health outcomes (depressive symptoms, resting HRV, and healthcare visits), and the degree to which gender moderates such effects. A total of 120 colorectal cancer (CRC) patients (60 male and 60 female) and their heterosexual caregiver (120 dyads) will participate. Understanding underlying biological and psycholgoical mechanisms is critical for identifying cancer caregivers and their patients who are at most risk for poor health due to their mutual stress regulation patterns. Findings of this project will be readily translated to development of novel interventions pertaining to effective and mutual management of stress in daily life and dyadic influences on health promotion. Those interventions will aim helping one another to better modulate and manage stress and optimizing beneficial effects of coregulation of cancer-related stress on better health. These tailored-and-targeted interventions will help caregivers identify when and how they should engage in stress self-management in the context of illness trajectory of their relative with cancer. They will also aim at reducing premature morbidity and mortality, particularly related to dysregulated cardiovascular, neuroendocrine, and immunologic systems, and psychological distress, among persons touched by cancer and other chronic illness, thereby improving public health.